Data Clippers: Bringing the Science Home

by Paul Gilster on September 21, 2010

I was fortunate enough to meet Joel Poncy (Thales Alenia Space, France) at last year’s deep space conference in Aosta, where he gave the audience the lowdown on an extraordinary mission concept, an orbiter of the Kuiper Belt object Haumea. Haumea is a tricky target, lacking an atmosphere that would allow aerobraking and pushing all our limits on propulsion and power generation. But Poncy’s team worked out a design using either electric or magneto-plasma technologies, assuming a gravity assist to shorten the journey for arrival around 2035.

In a later lunch conversation, Poncy talked to me about the benefit of probing the Kuiper Belt, and the collateral advances that such a mission would bring in terms of developing the orbiters, landers and deep-drilling capabilities we’ll need to explore planetary moons like Europa or Ganymede. Sometimes you choose targets, in other words, not only for their immediate payoff, but because they become part of the process of developing next generation tools. My two-part look at the Haumea mission, written last summer, begins here, with follow-up in this article the next day.

Solar Sails and Data Delivery

Now I see that Poncy is working on a unique solar sail concept he presented yesterday at the European Planetary Science Congress, which is taking place at the Pontifical University of Saint Thomas Aquinas in Rome. Poncy’s team has been studying ‘data clippers,’ spacecraft equipped with solar sails that are expressly designed to get large amounts of data back to Earth. And though we don’t often think of data return as a major problem, it becomes one as we push deeper into space and develop more sophisticated probes. Poncy puts it this way:

“Space-rated flash memories will soon be able to store the huge quantities of data needed for the global mapping of planetary bodies in high resolution. But a full high-res map of, say, Europa or Titan, would take several decades to download from a traditional orbiter, even using very large antennae. Downloading data is the major design driver for interplanetary missions. We think that data clippers would be a very efficient way of overcoming this bottleneck.”

The mention of Europa is particularly telling, given how much trouble we had with Galileo’s high-gain antenna, the lack of which caused the data flow from Europa and other Jovian targets to be much slower than anticipated. Moreover, a single orbiter with an equipment malfunction is, like Galileo, able to rely only on onboard backups and whatever software fixes can be sent.

So how do we proceed? The data-clipper would approach an orbiter, upload its stored data, and then make a flyby of the Earth, downloading the information to a station on the ground. Develop an entire of fleet of these vehicles and we could support planetary missions throughout the Solar System, including those interesting objects in the Kuiper Belt like Haumea. The work builds on recent solar sail successes like IKAROS but also looks ahead to magnetic sail possibilities. The latter would tap not solar photons but particles in the solar wind for their propulsive force. Needless to say, sail missions into the outer system would require hybrid propulsion, and it’s interesting to note that JAXA is already working on hybrid sail/ion propulsion concepts for a proposed Jupiter mission as a follow-on to IKAROS.

Moreover, data-clippers take advantage of the huge advances in miniaturization we’ve seen in digital electronics, allowing us vast amounts of data storage and long mission times with a properly shielded craft. Let me quote Poncy on this again:

“Using the Sun as a propulsion source has the considerable advantage of requiring no propellant on board. As long as the hardware doesn’t age too much and the spacecraft is maneuverable, the duration of the mission can be very long. The use of data clippers could lead to a valuable downsizing of exploration missions and lower ground operation costs — combined with a huge science return. The orbiting spacecraft would still download some samples of their data directly to Earth to enable real-time discoveries and interactive mission operations. But the bulk of the data is less urgent and is often processed by scientists much later. Data clippers could provide an economy delivery service from the outer Solar System, over and over again.”

The first data clipper mission could launch in the late 2020s, meaning that mission planners will want to include the technology in any thinking about future missions, the roadmap for which must be generated many years in advance. Think of fleets of these data harvesters bringing back the imagery and scientific data on planets, moons and objects of interest throughout the Solar System, without having to work with the minuscule bandwidth offered by current methods.

Different Kinds of Bandwidth

Sometimes, it turns out, just picking up an object and taking it somewhere is the best way to proceed. I remember a discussion with Vinton Cerf’s team on the ‘interplanetary Internet’ project out at the Jet Propulsion Laboratory some years back. I was taking voluminous notes as the team discussed what is called ‘disruption-tolerant networking’ (DTN), a way of using not a continuous connection (think FTP) but store-and-forward methods to hold data for later transmission. All this can be automated to reduce the load on Earth-based receivers.

And somewhere in that meeting, Cerf noted “You can’t underestimate the bandwidth of a pickup truck full of CDs driving from one coast to the other.” That’s bandwidth, too, getting the data where they need to be in large quantity and with low overhead. Poncy’s data clippers make me think of that pickup truck, only in this case it’s loaded not with CDs but with exotic planetary data, delivered in such quantity that we could set up serious mapping of objects that today are no more than bright spots in our surveys. All this is decades away — we have to get orbiters to such places — but the mid-term future could hold a planetary data bonanza delivered to our door.

The outer system probes can help determine the hydrogen/deuterium ratio. Enough of it may mean a source to support future fusion technologies. One interesting scheme for a starship is touched upon in http://www.centauri-dreams.org/?p=1142 which uses a large sphere of deuterium propellant.

The talk about physically transferring data around the solar system reminded me of this amusing story about one particular case of data transfer via physically sending the storage versus using the internet…

This is such a beautiful example of the concept that I want to print it here for those who don’t visit andy’s link. It’s from a BBC story:

“A carrier pigeon has transported a computer memory card between two two counties quicker than a computer on rural broadband could upload a video.
A pigeon has transported a computer memory card between two counties quicker than a rural computer could upload a five minute video to the web.

“In a race designed to highlight rural broadband problems campaigners began to upload the video as the bird left East Yorkshire for Lincolnshire.

“Rory the pigeon took about 80 minutes to get from Beverley to Wrangle, leaving the computer still running.

One big issue is having data redundancy, several of these “clippers” would have to be used at once, just to make sure the data isn’t lost by micro-meteor or radiation damage. My suggestion is why not use satellite “nodes” that are regenerative relays? a probe could be considerably smaller and would only need to transmit to the closest “node”. Each “node” would be then pass it to another node closer to Earth, and so on until it arrived here.

As we explore the outer planets, solar power gets weaker at R-squared so we might consider using isotopic power sources for long lived transmitter and computing power (think Voyager). The celestial mechanics would have to be taken into careful account if multiple missions are to be serviced. Some propulsion maneuvering might require onboard delta-V in addition to the light sail to allow for near planet/moon/asteroid maneuvering. The DTN Bundle Protocol would be adaptable to this kind of mission.

Agreed Vint, and nuclear electric options seem to be the best and only recourse for outer planet work to supplement the sail. We’re going to learn a lot from JAXA’s experience with their hybrid sail/ion propulsion mission to Jupiter. Amazing and instructive how the Voyagers just keep ticking…

This proposal brings to mind the suggestion that data might be best sent home via physical artifacts even over interstellar distances, presuming a very patient and long-lived science team, of course! The idea was (probably) discussed here on centauri-dreams, but now I can’t find the link. Does anyone else recall the idea, or better yet, does anyone have a link? The practice of transfering data via physical artifact is food for thought when contemplating SETI via radio telescope….

This highlights the need to develop semi-autonomous probes that utilize on-board software to “decide” which data to send home immediately (the most-interesting stuff) and which data to store locally for later use or transmission. If I remember correctly, I think the Kepler Mission uses on-board data analysis to discard some of the uninteresting data to lighten the transmission load back home…

Also: is optical data transmission via low-power lasers out of the question for outer system probes?… Or have we not yet developed the ability for that sort of precision involved in aligning a transmitter and receiver spaced 1 Billion miles or so apart? If it were possible, it might provide a good test of the technology (and maybe help spur its development) for later use on actual interstellar probes.

Joel Poncy (Thales Alenia Space) just wrote in with a clarification on data clippers and propulsion options. I’ll quote the message:

For Jupiter or Saturn a pure solar sail would be enough (no need for something else) because as you need to fall back towards Earth, you are basically looking for a transfer orbit between the inner system and the jovian or saturnian system and back. Actually in our scenario we start by going towards the Sun (at about 0.5 AU) to get the orbital energy of this “transfer” orbit” in the “sunlit zone”. We spend some time in the inner system so as to accelerate. But once this is achieved we want the transfer to be as “ballistic” as possible, so that the return leg from Europa fly-by to Earth fly-by goes as fast as possible (typ 3 to 4 years for getting the map of a Jovian moon back). You should not add thrust (or as little as possible) in this transfer orbit. If the sail is too large, or if you complement it with other propulsion, you will need to cancel the extra-thrust to go back to the inner system, otherwise you will go beyond Jupiter or Saturn and increase your (data) return time. You must leave Sun’s gravity act.

For more distant targets, you would need indeed to force the trajectory to accelerate the transportation but then we are back to the need to considerably improve the power-to-mass ratio of nuclear generators.

I agree with Scott that lasers are likely to get much more bang for the buck in the data transmission department than data clipper missions. Next after that would be a relay system, with no significant “physical carrying” involved. An example of the latter would be the “probe stream” we discussed before, a chain of “Voyagers” going out into interstellar space and relaying data between them.

I imagine it would be very difficult to maintain a regular shuttle orbit between Earth and an outer planet, anyway. At least, the round-trip frequency would be much larger at opposition than at conjunction. If it can be done with solar sails I don’t know, and I would like to know in what depth this issue was discussed.

I was also wondering, by the sounds of it, they use a “cyclic” orbit between Earth orbit and other orbits further away from the sun. Which means the clipper sail doesn’t slow down to rendezvous with the probe physically, but a burst of high bandwidth, high speed wireless link to transfer the data. If this is true, then there’s a need for the probe and clipper sail to be in vicinity to one another long enough to download gigs of data. Timing and velocities would have to be taken into account, high bandwidth, high speed data transmissions, if low powered, would be relatively short ranged, within a few miles. Also I repeat my concern of the need for redundancies, waiting 3-4 years is bad if we find that data is lost by the time it gets here and then having to get that data re-sent takes another 3-4 years isn’t feasible nor would sending multiple clipper sails.

Lasers have their own challenges. First, spacecraft aiming precision must be much higher since the target (that’s us) could be 1/100 or less than that for a narrow-beamed radio antenna. This is a direct consequence of the higher gain (lower dispersion). Second, the receiver end (that’s us, again) has noise to contend with. Depending on direction and frequency, radio sky noise can be under 10 K. With light you will have lots of high-temp point sources in the antenna (telescope) aperture that will create a few challenges in extracting the signal. Careful choice of laser wavelength will help.

None of this is to say that lasers shouldn’t be used, it’s just that you have to look at all the angles not just one attractive attribute.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last seven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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